Air pollutants including particulate matter and gases (e.g. VOCs) are known to have a wide range of negative health effects (including respiratory and cardiovascular diseases). Substances of biological origin, when present in air, are sometimes referred to as bio-aerosols. They include microorganisms and their fragments which can be toxigenic, allergenic and/or infectious. Respiratory diseases can be transmitted by inhalation of small airborne particles containing complete infectious microorganisms such as virus or bacteria aerosolized during coughing, sneezing and talking. Microorganism fragments (e.g. endotoxins and β-(1-3)-D-glucans) or by-products (e.g. microbial volatile organic compounds and mycotoxins) can cause toxic and allergic reactions.
The concentration of such particles in indoor air can be decreased using building ventilation and/or traditional air purifiers. In both cases, the clean air coming from the fresh air supply in the case of ventilation or from the air purifier outlet is mixed with the indoor air. Therefore, the pollutant concentration generally increases with increasing distance from the air outlet. Although the concentration gradient becomes smaller the closer the system is to its equilibrium, the general problem remains and is of particular importance for pollutants which are not being continuously emitted at a constant rate but in random, distinct patterns as for instance is the case of coughing and sneezing.
WO 2011/042801 A1 discloses methods and devices whereby a controlled personal breathing zone is maintained using temperature controlled laminar air flow (TLA) of filtered air. A substantially laminar, descending flow of filtered air is maintained with a velocity determined by the air-temperature difference between the supplied air and the ambient air at the level of the personal breathing zone. The air-temperature of the filtered supply air can be carefully adjusted to maintain the velocity-determining difference in air-temperature within the optimum range of 0.3 to 1° C. However, the disclosed methods and devices assume a stationary position of the person to which the laminar, descending flow of filtered air is delivered. However, people in stationary positions, e.g. sitting behind a desk or lying in bed, tend to move around to a certain degree, which movement may reduce the effectiveness of the targeted delivery of the filtered air, as the filtered air may no longer be delivered to the adjusted position of such people. Moreover, the need to detect and maintain the temperature of the delivered air adds complexity to such devices, which may be undesirable from as cost perspective as well as in a scenario where miniaturization of the device is an objective.
EP 2 687 789 A1 discloses an indoor unit of an air conditioning apparatus capable of achieving an air conditioning environment preferred by a user without operation of a remote control. Pre-stored face recognition information and user preferences are used to recognise the face of a user with an indoor imaging device and to blow conditioned air towards the user in accordance with the pre-stored preferences of the recognised user. Movement of the user's face may be tracked and at least one of the fan, refrigeration cycle and air flow direction adjustment device of the indoor unit may be controlled to send the conditioned air towards the determined position of the user. However, the tailoring of the delivery of such conditioned air may be further improved by considering parameters in addition to the location of the user.